


Pitiful Old Man

by Demoniaaa



Category: Undertale (Video Game)
Genre: Choking mention, Fluff, Hurt/Comfort, Kissing, M/M, Mentions of Dubcon, Tentacles, drool
Language: English
Status: In-Progress
Published: 2016-01-07
Updated: 2016-01-13
Packaged: 2018-05-12 07:47:43
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 2,877
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5658340
Author URL: https://archiveofourown.org/users/Demoniaaa/pseuds/Demoniaaa
Summary: <blockquote class="userstuff">
              <p>Frisk always went down to the Underground, even four years later. Though, something is new on their latest journey through. Frisk finds a grey door in the middle of Waterfall, and an even stranger man lost to the void behind it. Recognizing Gaster as an old friend of Sans, they decide to reunite the two.</p>
            </blockquote>





	1. Chapter 1

Four years. It had been four years since the underground had gone empty. Though every four months, Frisk would return with Toriel to see if a certain goat child or flower was there. It was the same as it always was. Empty, and quiet, devoid of anything new. It was the same in Waterfall. Only now, instead of the crackling of lava in Hotland or the crunch of snow beneath their feet in Snowdin, the air held the soft whispers of echo flowers and a distant twinkling of a music box. Something this time felt different though, the air held something more than sound, as if dread hung heavy on the pair of shoulders as they walked. It was as if something followed them with no clear purpose in mind. Just to observe. Frisk, ever curious child that they were, decided to look around Waterfall further. They usually just went the straight path, but now? They wanted to find the source of this dread. This feeling had never been here before..

 

Frisk and Toriel walked for what felt like hours, until they stumbled upon a grey door in the middle of the damp and murky pathway. Toriel held Frisk’s hand a little tighter.

 

“My child, perhaps we should head back home..” Frisk looked up at her with a slight frown. They wanted to find the source.

 

“Mom..” They pursed their lips, “i’ll be alright. I've dealt with worse.” They gave Toriel a knowing smile.  She sighed.

 

“Alright. But I'm staying right outside this door. If it is another pathway I want you to come right back. I trust you.” Slowly, Frisk let go of her hand and put it to the door’s knob. With a turn and a pull they opened the door.

 

It was barren. White. Frisk took a step forward and the door slammed shut behind them. They quickly glanced back before they looked around and froze at the man in the corner. A black, amorphous blob that bubbled as it stood, tall and lean and dripping. A head formed, turning to the side as a white pupil in a sea of black iris looked back at the child.

 

 **_“WHAT IS A HUMAN CHILD DOING IN THE UNDERGROUND?”_ **  It spoke, a rich voice that sounded as if it was both crackling and underwater, the slightest bit of black slime dripping down his chin. It spun around, and with surprising quickness leapt at Frisk, body stretching to curl around the child but never touching. The creature looked at Frisk with a deranged smile, a crack forming from both eye sockets. Then, something clicks. Frisk knew of Sans’ past to some degree, and from the photos they had seen, recognized this man from them. In every photo he was almost non existent, blurry or scratched, sometimes even a hole in an old photograph, but staring at him now solidified it. Sans knew him. Suddenly, hands appeared, grasping at Frisk, around their arms, one placed at their neck but never squeezing.

 

 **_“I HAVE SEEN WHAT YOU DO. SEEN WHAT YOU HAVE DONE FOR ALL OF THESE MONSTERS, EVEN THE PRINCE, AND I MUST SAY, I AM IMPRESSED. EVEN NOW I SEE IT, THAT LOOK IN YOUR EYE CHILD. WHAT YOU PLAN.”_ ** The creature let out a laugh, bubbling out from his throat and Frisk could see his face crack a little more. **_“THERE IS NO WAY TO SAVE WHAT HAS ALREADY BEEN DESTROYED, CHILD, BUT I ENCOURAGE YOU TO GIVE IT YOUR BEST EFFORT.”_ **

 

*This shouldn't be happening.

*W.D Gaster ----.9 ----. ATK 99----. ----. DEF

Former .-. --- -.-- .- .-.. scientist. - .... . / ...- --- .. -.. / --- .-- -. ... / .... .. -- / -. --- .-- .-.-.-

 

*You tell Gaster you know who he is. He laughs.

 

**_“YOU SAY THAT AS IF THAT HAS ANY SWAY IN THIS.”_ **

 

*You give Gaster a small smile. He cannot look at you.

 

**_“CHILD. YOU CAN NOT CHANGE FATE.”_ **

 

*You tell Gaster that you know Sans. His smile falters but his head whips back to look at you.

 

**_“YOU… KNOW HIM?”_ **

 

*You tell Gaster that Sans thinks about him. His form falters.

 

**_“ST-STOP. YOU DO NOT KNOW WHAT YOU DABBLE IN.”_ **

 

*You tell Gaster that Sans still misses him. Gaster puts his hands on his head, a whimper escapes him as his body bubbles furiously.

 

**_“E-ENOUGH…”_ **

 

*You tell Gaster that Sans still loves him.

 

**_“STOP IT!!”_ **

 

Gaster let go of Frisk, his form sinking in on itself as the extra hands that held Frisk previously disappeared and black tears pooled in his eyes and rolled down his cheeks. So many painful memories came back in that instant; the void has made him unstable, and so whenever he slipped into timelines to see Sans, everything went sour. He'd hurt his Sans out of frustration, anger, jealousy, arousal. Any emotion he held at the time of the encounter. He could still see Sans choked by his hands underneath him when he closed his eyes, as if they were burned into his eyelids. Gaster let out a yell, ripping up from his throat as sorrow wracked whatever body he still held. He held his head, eyes shut tight as he tried to make the memories go away.

 

 **_“WHAT HAVE YOU DONE, CHILD…?”_ ** He breathed, **_“LEAVE HERE. I REFUSE TO SPEAK TO A CHILD SUCH AS YOU.”_ ** He looked at Frisk with a look of both fear and pure rage, black tears pooling in his eyes and rolling down white cheeks. Frisk had taken a step forward, gasping when black tentacles grabbed them and forced them out of the door. Toriel gasped as she saw Frisk stumble out.

 

“F-Frisk! Are you okay?” She asked with worry. Frisk rubbed their head and nodded, looking back and seeing the door was locked. “What happened in there?” She asked, glancing at the door.

 

“I’ll explain on the way home. Sans is home tonight, right?” They asked with such an urgency. Toriel blinked in surprise, but nodded.

 

“Yes, he'll be home tonight. What's wrong?” She frowned. Frisk sighed, rubbing their head.

 

“It's a long story. Come on.” They murmured, the two heading back up to the surface.

\--

 

Frisk hasn't told Sans what they had seen down in the underground when they got back or even after dinner. When they mustered up the ever needed courage, it was around midnight. They snuck into Sans’ room, quietly shutting the door and walking up to the big lump under the thin sheets on a bare mattress. Slowly, Frisk put a hand to the lump, gently shaking it.

 

“Sans?” They whispered. “Are… Are you up?” Frisk watched as Sans sat up and stretched, rubbing his eyes and letting out a large yawn.

 

“Well I mean I am now.” Sans chuckled softly, “You okay, kiddo? Bad dream?” He moved and patted a spot next to him so Frisk could sit. He watched as Frisk climbed up onto the bed, taking a deep breath.

 

“You know how I said that if me and mom found anything important in the Underground I’d tell you?” They asked. “Well I uh.. Found a door in Waterfall.” They went on to tell of what happened; the strange gooey man and his panicked ramblings, even giving Sans the name. Sans froze when Frisk told him his name. A shake escaped him, which transformed into a chuckle, and then into a laugh.

 

“Th-That sounds like a pretty _gast_ ly situation, are you alright? He didn't hurt you?” He asked once he calmed down. Frisk nodded, confused out of their wits? Maybe. But hurt? Not at all. They might have hurt Gaster more than Faster hurt them. “You… You know where he is?” His voice held such a sliver of hope. Frisk nodded. “Then… Then we can leave in the morning...” He pet Frisk’s head, watching Frisk nod and lay down. Sans sighed, joining them before laying down.


	2. Chapter 2

Sans was uneasy the entire way back down. He was usually the one to join Frisk on these little missions, but it had never had this much weight to them. He had spent so many years trying to bring Gaster back from wherever he had gone. When Gaster had passed he had never turned into dust. The moment he had fallen into the core, everyone had forgotten. Everyone but him. He could feel his bones rattle, the bottoms of his slippers becoming damp as they walked into Waterfall.

 

“Sans? Was… Was Gaster important?” Frisk asked, their voice breaking the silence. Sans had jumped a little at the sudden voice, but just swallowed thick and nodded.

 

“He was… Everything..” Sans sighed. “After Gaster was gone, Papyrus was all I had. I just… I miss him so much, ya know?” He looked over at Frisk. “Sometimes.. Gaster would show up, like he could get into the timeline somehow, but he never stayed for too long.” Frisk held his hand at this point. Sans was trembling, rattling, but Frisk wanted to calm him down. They had never seen Sans so uneasy, or maybe it was fear Frisk was seeing, for as long as they had known him. 

 

“So… What was he like? Before he was gone, I mean..” Frisk asked, maybe talking about the good things would help ease him. Sans sighed, rubbing one eye socket.

 

“He was… amazing… and so smart, that guy built the core!” Sans smiled. “Heh, most times, when I was working with him, We would work way into the night, like three or four. I'd pass out at the workbench and wake up in my own bed, the doc in the kitchen with some tea for the both of us when I came down. ‘Do not work yourself too hard, Sans. You could get sick. I need my best assistant by my side..’ He’d tell me..” Frisk listened with such happiness, Gaster sounded like the opposite of what they had seen in that grey room. A piece of Frisk worried that things might go bad when the two saw each other again, but they had to try. They were starting to understand why Sans always forced his smiles when it wasn't with Papyrus, understand all the secrets Sans held. Frisk looked around, spotting the door and pointing at it.

 

“He was in there..” Frisk said. Sans felt his body move before he thought it, even with Frisk still holding his hand, like it weighed him down and grounded him. The two went to the door, and Frisk, the concerned little twelve year old that they were, looked up at Sans. “You gonna be okay?” Sans took a deep breath and put his hand to the knob. 

 

“Yeah.. I’m gonna be fine, Frisk.” Part of him prayed it was locked, so then maybe he didn't have to see what horror his Gaster had become. He knew how bad Gaster was, somehow when Frisk met him, they had seen none of it. He was worried Gaster might hurt Frisk. But alas, the knob turned just as easily as any other. Sans pulled the door open, Frisk and Sans walking inside. The door slammed shut behind him. If Sans had any blood, he was sure it would have gone cold when he saw Gaster, bubbling and shaking in the barren room. Frisk let go of his hand, looking over at him. 

 

“Wait here.” They whispered, running over to Gaster. “Mr Gaster?” They spoke, the blob jolting for a moment. It stretched up to stand, his head appearing and he leaned down to look at Frisk. He looked upset.

 

**_“Child… Why have you returned?”_ **  He sounded calmer, Frisk smiling at that. They raised their hands and held Gaster’s cheeks. 

 

“I brought a friend. Someone who I think really wants to see you again.” They said, smiling. Gaster raised an eyebrow. 

 

**_“What? Who do you…”_ ** He looked over, freezing when he saw Sans.  **_“mean…”_ **

 

“Hey, G…” Sans murmured, giving a sheepish smile and waving, one hand stuffed into his pocket. Gaster backed away, black tears forming and his mouth hung open in pure shock. 

 

**_“WHAT IS HE DOING HERE??”_ ** Gaster sputtered,  **_“CHILD, THIS BETTER NOT BE SOME TRICK BECAUSE I SWEAR..!”_ ** He paused when Frisk gently hugged him. 

 

“It's okay! Please!” Frisk cried, trying to calm the very frightened scientist. Gaster had started making a whining noise, his eyes closed but they quickly sprung open when the memories flashed before him, even when he tried to let go.

 

_ Sans writhed beneath him, pained and pleasured whines escaping him as Gaster touched him with multiple hands. Fingers hooked in his ribs and a hand around his spine and his neck. Multiple slimy black tentacles rising up from the shadows on the floor and plunging inside his assistant and hearing the pleasured moan escape Sans, meeting his eyes as Sans begged for more. _

 

“We can help you. The barrier… It's, It’s gone. You can come up with us!” Frisk looked at the scientist. Gaster gasped. 

 

**_“No… No I-I can not go. I… I am supposed to be forgotten.”_ ** Gaster quickly shook his head.

 

“Gaster, the surface is different now.” Sans spoke up, though he couldn't meet Gaster’s stare. Sans gasped as Gaster moved like lightning, appearing in front of him and picking him up, two hands hooked into his arm pits to hold him up. 

 

**_“S-Sans..”_ ** Gaster muttered, he was bubbling and frowned at the sight of his assistant. 

 

“Just.. Trust me, okay? Like you always do.” He gave a sheepish smile. It wasn't like Gaster was intentionally a bad guy. But if someone spends years in the blackness of the void, they're bound to lose it. Sure the unstable emotions and violent intimacy with no after care was nothing to ignore, but Sans knew he couldn't really be angry at him for it, and he didn't want to be angry. Add in the skeleton Gaster was practically a soulmate with to the mix, and it was bound to create tension. The only fear Sans really had was if Gaster took that unstable energy out on Frisk, he had the endurance to deal with Gaster, he doubted Frisk did. Gaster taught Sans all he knows about fighting. He brought a shaky hand to Gaster’s cheek. “Come on, G, at least do it for me.” He smiled at him. Gaster took a shaky breath, slowly pulling Sans into his arms. It was probably one of the weirdest sensations Sans had; it felt like being enveloped in many many pillows, but they were slimy and wet and still smelled like the cheap cologne Gaster had always bought that always reminded him of the smell in the lab’s lobby and the fragrance of an echo flower. It held such familiarity that Sans didn't realise he was crying until he pulled away and saw a wet spot on the white turtleneck Gaster wore. Gaster took a deep breath but nodded.

 

**_“For you, Sans. I will try.”_ **  His smile was crooked and it sent a shudder through Sans. Gaster set him back down, holding Sans’ hand. Sans looked over at Frisk, who grinned and gave him a thumbs up. The group began to walk out, Gaster being oddly calm. Just to fill the silence Frisk and Sans decided to fill in Gaster about what's gone on since he had been missing. 

 

“Yeah, it's been crazy, a-and Paps is-”

 

**_“Papyrus is doing rather well, right? I always worried about that skeleton when I was in the void...”_ **  Gaster spoke up, Sans smiling and nodding. 

 

“He's doing great!” Sans said with an odd cheer. The group talked until they got to the surface. Gaster had paused at the mouth of the exit. He looked up at the sky with a strange awe. Sans looked over at Gaster, his hold on his hand tightening a little. Sans looked at Frisk. “Do you… Know if anyone will remember him? Tori might know him, and Alphys will.” Frisk merely shrugged with a slight frown. There was really no way to tell at the moment. Sans was the only one that remembered him before all this, and Frisk didn't know him prior. Sans sighed and looked up at the awe struck scientist. “You should see how it is at night, G, Pretty cool.” Sans said, causing Gaster to jolt from his stupor and look down at Sans. 

 

**_“You will have to show me sometime, Sans.”_ **  Gaster spoke, a bubbling laugh coming up from him. The group started waking again, heading to Sans’ place. Outside, Papyrus was just returning home as well, most likely from Undyne’s. Papyrus looked over, smiling. 

 

“Sans! Hello! Who is your very tall friend?” He asked, striding over to them. At first a twinge of pain struck Sans, but then the smaller brother remembered Papyrus never formally met Gaster, so there would be no recognition. Especially not the way Gaster looked now. If Papyrus  _ had _ recognized him, that may have been room for concern. That would have meant Gaster visited him too. Papyrus let them all in, just happy to see Sans had a new friend. 

 

**_“I am Dr. WD Gaster, but you may call me Gaster.”_ ** Gaster shook Papyrus’ hand, trying to give his best smile but it came out crooked and cracked. Papyrus didn't seem phased in the least, merely excited to meet someone new. Gaster looked at Sans when Papyrus left to go cook dinner. 

 

“Not bad..” Sans smiled, giving him a little thumbs up. 


End file.
